Impact wrench



IMPACT WRENCH Sheet Filed Oct. 12, 1967 INVENTORF 2A YMONV J. SCH/F0452 W/LL/AM K. WALL/Me BY J t ylw M ATTORNEY Feb. 18, 1969 R. J. SCHAEDLER ET AL 3,428,137

IMPACT WRENCH Filed Oct. 12, 1967 Sheet 2 WILL/14M K- n ALLAKE ATTORNEY Feb. 18, 1969 R. .1. SCHAEDLER ET Al. 3,428,137

IMPACT WRENCH Filed Oct. 12, 1967 Sheet 3 of 5 INVENTORS W/L 4 09M 4 WA: 4 4:5

ATTQRN EY United States Patent Office 3,428,137 Patented Feb. 18, 1969 ABSTRACT OF THE DISCLOSURE A reversible impact wrench having a high ratio of power output relative to its size and weight. The driving shaft of the rotor of the wrench is coupled to a dog-hammer having a recess in its rear in which the coupling is compactly telescoped. The dog-hammer is movable axially relative to the coupling against a return spring by ball cam means into rotary impacting relation with an anvil carrying a wrench socket. This is unlike conventional impact wrenches in which a conventional dog is movable into such impact relation relative to a driving hammer frame of heavy mass. The dog-hammer carries a symmetrical cam as a means of driving selectively in either direction a ball follower about a track relative to a symmetrical cam tooth associated with the anvil. The arrangement is such that the dog-hammer and its cam are cooperable with the ball and cam tooth so that it is axially accelerated clear of the ball during camming action. Because of the nature of the track and cam elements, the ball cannot possibly become trapped between the cam elements upon return of the dog-hammer following impact. If it were to become trapped, the jaws of the doghammer and anvil would be subject to possible interlocking and malfunctioning. The wrench also includes means for diverting reactionary thrusts of tool operation from the rotor to the general housing.

Background of the invention This invention relates to the art of rotary impact wrenches of a type in which a rotating member is periodically reciprocable into and out of rotary impacting relation with an anvil portion of a torque output shaft.

The design of the wrench of the present invention represents a' decided technical advance in the art. It is such that the ratio of power output to the size and weight of the wrench is relatively higher than that of conventional Wrenches. Because of the improved design, the ratio of torque available to accelerate rotating parts of the wrench compared to the inertia of such parts has been materially increased for a given motor size with consequent increased power output.

These advantages are due primarily to an improved hammer and anvil impacting arrangement from which the conventional heavy rotating hammer frame mass and its associated inertial drag upon the motor have been eliminated. Improvements have also been made in the camming means of the wrench. It includes a rolling ball and cooperating cam track arrangement which functions to cause highly accelerated axial movement and forceful rotary impacting engagement of a rotating dog-hammer with a torque output anvil member. The elements of the cam track cooperate with one another and with the ball to insure a smooth return of the dog-hammer following an impacting action without interference with the ball. Improvement has also been made in the supporting arrangement of the driving rotor whereby operating thrusts of the impacting elements are diverted to the general housing of the tool and thus prevented from reaching and exerting an undesirable drag upon the rotor.

Summary of the invention In accordance with the invention, there is provided an impact wrench comprising a rotor drive shaft, a driven torque output anvil means, a dog-hammer drivably connected with the shaft having relative axial movement into and out of rotary impacting engagement with the anvil means, a spring constantly urging the dog-hammer to a normally retracted position out of such engagement, camming means operable as a consequence of rotation of the dog-hammer relative to the anvil means to cause axial movement of the dog-hammer into such engagement against the resistance of the spring, an axial recess in the rear of the dog-hammer having axially extending splines, a coupling relatively lighter in weight than the dog-hammer having an internal driven spline connection at its rear with the drive shaft and having a forwardly extending portion telescoped in the recess having splines with which the splines of the dog-hammer have slidable engagement permitting relative axial movement of the dog-hammer, and means restraining the coupling against axial movement with the dog-hammer.

Brief description of drawing FIG. 1 is a longitudinal section of an impact wrench embodying the invention;

FIG. 2 is a section on line 22 of FIG. 1;

FIG. 3 is a rear end view of the anvil;

FIG. 4 is a front end view of the dog-hammer;

FIG. 5 is a detail of the anvil cam shaft sectioned in part;

FIG. 6 is a left end view of FIG. 5;

FIG. 7 is a profile view of the anvil cam tooth;

FIG. 8 is a detail in longitudinal section of the dogcam taken on line 8-8 of FIG. 9;

FIG. 9 is a right end view of FIG. 8;

FIG. 10 is a profile view of the land of the dog-cam;

FIGS. 1l14 show in schematic the events of a camming cycle in which;

FIG. 11 shows the relative positions of the camming elements at the start of a cycle;

FIG. 12 shows the position of the ball and dog-cam at the start of the movement of the ball up a slope of the anvil cam tooth;

FIG. 13 shows the position of the cam elements prior to the ball being shot over the anvil cam tooth; and

FIG. 14 illustrates the trajectory of the ball upon being shot over the anvil cam tooth, and the consequent impacting action of the jaws of the dog-hammer with the jaws of the anvil.

Description of preferred embodiment The illustrated pneumatically powered impact wrench embodying the invention includes a general housing comprising in order a front section 11, an intermediate motor section 12 and a live air handle section 13, all fixed to one another in end-to-end relation.

A motor unit 14 is housed in the intermediate section. It is of a conventional pneumatic reversible type having a stationary liner 15 defining a chamber 16 in which a pneumatically powered rotor 17 is eccentrically arranged. The rotor has the usual radially slidable blades 18 which sweep the wall of the liner as the rotor turns. Opposite ends of the rotor bear upon stationary circular closure heads or end plates 19 and 21 abutting opposite ends of the liner. The front plate 19 is seated upon an annular shoulder 22 of the housing section 12; the rear plate 21 abuts an overlying annular face 23 of the handle section 13. The rotor is supported for rotation by means of oppositely extending shaft ends 24 and 25 respectively journaled in bearings 26 and 27. Bearing 26 is seated in an axial recess of the front plate 19. Thrusts imparted to this bearing during operation of the tool are transmitted through its outer race to the end plate 19, and are absorbed by the liner 15 and general housing.

The handle section 13 is fitted with a hand operable throttle valve 31 which is connectible by means of an inlet fitting 32 with an external source of live air. The valve controls flow of operating air through passage means 33 leading to the rotor chamber 16. The rotor is reversible. A conventional hand controlled reversing valve 34 arranged in a chamber 35 intermediately of the passage means 33 is selectively operable to direct live air to either a positive or negative area of the rotor chamber.

The rotor is drivingly coupled to a cylindrical doghammer 36. In this coupling arrangement, the front shaft end 24 of the rotor has a longitudinally splined driving connection at 37 with an open-ended coupling 39. The coupling is telescoped in an annular rear recess 41 of the dog-hammer. The coupling has longitudinal external splines with which complementary internal splines provided in the recess of the dog-hammer 36 are slidably engaged, as at 42, whereby rotation of the rotor is transmitted through the coupling to the dog-hammer, and whereby the dog-hammer is axially slidable relative to the coupling.

Cam means 43 is incorporated in the tool. It is confined in the interior of the coupling 39 within the rear recess 41 of the dog-hammer. Its function is to force the dog-hammer axially against the resistance of a return spring 44 during each revolution of the dog-hammer so as to bring the radial sides of a pair of dogs or jaws 45 projecting axially (FIGS. 1, 4, 14) from a forward wall of the dog-hammer into rotary impacting relation with the sides of a pair of radial jaws 46 of an anvil member 47 (FIGS. 1, 3).

The anvil member 47 is supported for rotation by means of a shank portion 48 in a bushing 49 fixed in the housing section 11. An external part of the shank is adapted for splined engagement with a wrench socket 52 (broken line). Suitable socket retaining means 53 is provided to retain the socket upon the shank. The socket is designed for engagement with a threaded fastener such as a multi-sided nut or bolt head.

An anvil cam shaft or spindle 54 (FIGS. 1, is seated at one end in an axial recess 55 of the anvil member and is made unitary with the latter by means of a longitudinally splined connection 56. An axially extending pilot portion 57 at the rear of the cam shaft is journaled in a thrust collar 58. The latter in turn has a hub 59 journaled in an axial recess of the rotor shaft 24.

The collar 58 extends radially beyond the rotor shaft so as to abut upon a forward face of an internal shoulder 61 of coupling 39. The rear end of the coupling abuts the inner race of the thrust bearing 26. The shoulder 61 spaces the collar 58 slightly clear of the end face of the rotor shaft. By means of this arrangement, the coupling is restrained against axially moving with the dog-hammer; and axial thrusts imparted to the collar during operation of the tool are transmitted to the thrust bearing 26 to be absorbed by the end plate 19, the liner 15 and the general housing of the tool. The rotor is thus spared from such thrust forces, whereby its useful life is prolonged and the drag which might otherwise be imparted by such thrusts to the rotor is avoided.

The return spring 44 encircles the cam shaft 54. It is seated at one end against an axially recessed shoulder 63 of the anvil member; and its opposite end presses upon a spring cup 64. The latter is slidable along the cam shaft and overlies an adjacent forward face of the dog-hammer 36. The spring acts through the cup 64 to bias the doghammer to a retracted normal position, as in FIG. 1, wherein its jaws 45 are disengaged from and are axially clear of the anvil jaws 46. In this retracted position of the dog-hammer, its recessed back wall 60 abuts the front end of coupling 39.

The camming means 43 (FIGS. 1, 2, 5-7) includes an annular flange 65 formed upon the cam shaft 54 forwardly of the pilot 57. The rear face of the flange bears in part upon the thrust collar 58. An annular groove 66 formed in a forward face of the flange is concentric with the axis of the cam shaft. This groove extends in its radial dimension to the periphery of the flange. The groove is interrupted in its continuity by means of a cam tooth 67 projecting axially substantially to the extent of the radius of the groove. Tooth 67 is defined by a pair of symmetrical slopes 68 and 68a culminating in a small outside radiused crest 69.

The camming means 43 further includes (FIGS. 1, 2, 8-1-0) an annular hammer cam element 71. The latter is sleeved upon the cam shaft 54 for relative rotation and axial sliding movement. It has a cylindrical stem 72 made unitary with the dog-hammer by means of a longitudinally splined axial connection 73 internally of the dog-hammer. The dog-hammer and the hammer can have axial and rotative movement as a unit. Rearwardly of the stem 72, the hammer cam has an annular enlarged body 74 which abuts the recessed back wall 60 of the dog-hammer and is fully received within the interior of a forward portion or skirt 76 of the coupling 39 in the retracted condition of the dog-hammer, as in FIG. 1. The body 74 is provided with a recess 77 in its rear, the side wall of which surrounds the flange 65 of the cam shaft. The bottom of recess 77 is formed with an annular groove 78 (FIGS. 2, 8, 9) which is interrupted in its continuity by means of a flat crest or land 79, the axial projection of which corresponds to the radius of the groove 78. The ends of the groove, which are also the ends of land 79, are defined by means of a pair of symmetrical inside radiused shoulders 81 and 81a which are longer in their incline than the slopes 68, 68a of the anvil cam tooth 67. Groove 78 extends for about 240 and is in parallel opposed concentric relation to the groove 66 formed in the cam shaft flange 65. The land 79 extends for about 120.

The opposed grooves 86 and 78 define between them (FIGS. 1, 2, 8-14) a ball track in which a steel ball 83 rolls. The inner diameter of the track is defined by the periphery of the cam shaft 54. The outer diameter of the track is defined by an arcuate wall segment 84 defining a portion of the side wall of the recess 77 of the hammer cam body. The land 79 is backed by an arcuate wall segment 85 defining a further portion of the side wall of recess 77. The inner radius of wall segment 85 is relatively less than that of segment 84 so that wall 85 is relatively thicker and projects radially inwardly of the outer edge of groove 78, as best appears in FIG. 9. The ends of the segment 85 are in axial extension of the end shoulders 81 and 81a 50 as to provide stops 86 and 86a for the corresponding ends of the ball track, which stops together with the shoulders 81 and 81a define the limits of angular travel of the ball relative to the hammer cam. The inner wall surface 85 of the hammer cam bears upon the periphery of flange 65 for relative rotation.

In this arrangement of the cam elements, the ball 83 is caused to be pushed about the track by means of one or the other of the shoulders 81 or 81a of land 79, accordingly, as the dog-hammer rotates in one direction or the other. In the fully retracted condition of the dogharnmer, the land 79 and the cam tooth 67 are axially spaced from one another by a slight clearance, as at 82 in FIG. 11, so that the one will not strike the other during relative rotation. This spacing is determined by means of the axial length of coupling 39 which lies in abutment with the recessed back wall 60 of the dog-hammer.

When the anvil cam shaft 54 is stationary, as it will be when the work offers a predetermined degree of torque resistance, the hammer cam 71 rotates under the drive of the dog-hammer relative to flange 65 and one of the shoulders 81 or 81a pushes the ball 83 about the track. Eventually, the ball is forced up and shot over the crest 69 of the cam tooth 67 into the ball track beyond the cam tooth, the trajectory of the ball being indicated by the arrow T in FIG. 14. The dog-hammer attains a high velocity as it rotates. At the time the hammer cam is forcing the ball over the cam tooth, the hammer cam together with the dog-hammer are being cammed axially as a unit relative to the flange 65 of the cam shaft against the resistance of the spring 44 to bring the sides of the dog-hammer jaws 45 into forceful rotary impacting relation with the sides of the anvil jaws 46. In this camming action, the dog-hammer is caused to move axially at high acceleration clear of the ball because of the high velocity of rotation of the dog-hammer. The axial depth of possible engagement of the jaws of the dog-hammer with those of the anvil is such that the side wall 84 of the body 74 of the hammer cam will never move axially free of the coupling 39. Accordingly, the ball is at all times during its rolling movement confined in the ball track. The stops 86 and 86a defined by the radially thickened portion 85 at the back of the land 79 prevent the ball from rolling out of the groove 78 onto the land as the cam elements separate. Accordingly, the ball is confined at all times in the extent of its rolling movement to the limits of the hammer cam groove 78.

Immediately following impact, the spring 44 re-expands to retract or return the dog-hammer and hammer cam as a unit to normal position, and rotation of the hammer continues as before to again drive the ball about the track for a repeat camming action. Since there is a slight looseness between the ball and opposed surfaces 87 and 84- respectively of the cam shaft and the surrounding wall of the hammer cam body, the ball rolls freely about the track following its movement over the cam tooth 67. The force with which the ball is shot over the cam tooh may carry it completely around the ball track. However, as mentioned earlier, it will be limited in this movement by either the stop 86 or 86a so that it cannot possibly roll out of the groove 78 to become trapped axially between the land 79 and the bottom of groove 66 of flange 65 whenthe dog-hammer is returned. If it were to become trapped, the jaws of the dog-hammer and anvil would be subject to possible interlocking and malfunctioning.

As earlier mentioned, thrusts imparted by the returning dog-hammer and hammer cam respectively to the coupling 39 and thrust collar 58 are transmitted through the inner race of the thrust bearing 26 to be absorbed by the end plate 19, liner 15 and the general housing of the tool. Similarly, thrusts imparted by the cam shaft 54 to the thrust collar 58 are also transmitted to the thrust bearing 26 to be absorbed by the general housing. Ac cordingly, very little of the thrusts developing during operation of the tool are transmitted to the rotor.

The coupling 39, being positioned between the bearing 26 and the recessed wall 60 of the dog-hammer, determines the returned position of the latter. This returned position is such that the 'ball 83 is not under axial compression between the bottoms 78 and 66 of the ball track so that the ball has a slight axial looseness in the track. This is of advantage in that the coupling is caused to receive the thrusts of the dog-hammer as the latter returns following an impacting action and prevents such thrusts from being transmitted to the ball.

FIGS. 11-14 schematically illustrate in greater detail the events of the camming action. The dog-hammer 36 is indicated in FIG. 11 as rotating in a positive direction. The ball 83 has obtained a position at the base of a shoulder 81 of the hammer cam and is being pushed around the ball track preparatory to a camming action.

Eventually, the ball will attain the position shown in FIG. 12 at the base of the rear slope 68a of the anvil cam tooth 67. As the hammer cam continues rotating, it rolls the ball up the slope 68a and in doing so is itself cammed or forced axially away to carry the dog-hammer with it. The dog-hammer and hammer cam are at this time rotating at high velocity. At about the time the ball attains the position shown in FIG. 13, it will be upon the starting or initial portion of the outside radius or the crest 69 of the cam tooth and it will be engaged at a diametrically opposed area by the high end 89 of the inside radius area of the hammer cam shoulder 81. In this position, the ball will be loaded under opposed nonparallel surfaces. Upon this condition being obtained, the ball is shot or forcefully slipped over the crest 69 of the cam tooth 67 by the shoulder 81 of the hammer cam in a trajectory path indicated by the arrow T in FIG. 14; and simultaneously the hammer cam and doghammer rotating at this time at high velocity are accelerated axially as a unit to impact the jaws 45 of the dogham-mer with those 46 of the anvil. In this action, the hammer cam moves axially clear of the ball and the ball rolls forwardly and freely beyond the cam tooth 67 into the ball track. The extent of axial movement of the doghammer relative to the cam tooth is such as to carry the land 79 a distance from the cam tooth 67 substantially greater than the diameter of the ball. Immediately following impact, the hammer cam and dog-hammer are axially returned by spring 44 out of impacting relation; and forward rotation of the hammer cam and dog-hammer is resumed. As rotation is resumed, the land 79 of the hammer cam is carried clear over the crest 69 of the cam tooth and eventually the forward shoulder 81 of the hammer cam re-engages the ball as in FIG. 11 to again roll it about the track preparatory to a repeat impacting action.

When the dog-hammer is operating ina negative or reverse direction, the other shoulder 81a of land 79 functions to push the ball about the track toward the other slope 68 of the anvil cam tooth 67 It is to be also noted that the dog-hammer replaces the usual heavy elongated hammer frame mass and slidable dog combination known from conventional prior art devices. Thus a tool of relatively lighter weight is provided. The elimination of the heavy hammer frame mass avoids the attendant inertial drag of the mass upon the rotor. Its elimination also enables a more compact and axially shorter overall housing to be employed, as indicated in the present invention.

What is claimed is:

1. An impact wrench comprising a rotor drive shaft, a driven torque output anvil means, a dog-hammer drivably connected with the shaft having relative axial movement into and out of rotary impacting engagement with the anvil means, a spring constantly urging the dog-hammer to a normally retracted position out of such engagement, camming means operable as a consequence of rotation of the dog-hammer relative to the anvil means to cause axial movement of the dog-hammer into such engagement against the resistance of the spring, an axial recess in the rear of the dog-hammer having axially extending splines, a coupling relatively lighter in weight than the dog-hammer having an internal driven spline connection at its rear with the drive shaft and having a forwardly extending skirt telescoped in the recess provided with splines with which the splines of the dog-hammer have slidable engagement permitting relative axial movement of the doghammer, and means restraining the coupling against axial movement with the dog-hammer.

2. An impact wrench as in claim 1, wherein a thrust bearing supports the drive shaft for rotation, a forward end of the coupling abuts the bottom of the recess in the retracted condition of the dog-hammer, a rear end of the coupling constantly abuts the thrust bearing, and a rotor housing supports the thrust bearing, the thrust bearing being the sole abutment blocking rearward axial movement of the coupling relative to the drive shaft so that axial thrusts imparted to the coupling by the dog-hammer under the urging of the spring are transmitted primarily to the thrust bearing and rotor housing and away from the drive shaft.

3. An impact wrench as in claim 1, wherein the anvil means includes a spindle extending axially rearward through the dog-hammer into the interior of the skirt of the coupling having an annular flange disposed in said interior, and the camming means is confined between the flange and the bottom of the recess of the dog-hammer.

4. An impact wrench as in claim 3, wherein the camming means includes a cam element carried by the doghammer within its recess, a ball track defined between the cam element and the flange of the anvil means, a symmetrical cam tooth on the flange projecting axially into the track, a ball rollable about the track, and an arcuate land having symmetrical inside radiused shoulders at its ends extending axially from the cam element into the ball track, one of the shoulders having driving cooperation with the ball as the dog-hammer rotates in a selected direction relative to the anvil means so as to force the ball about the track and over the cam tooth and as a consequence force the dog-hammer axially against the resistance of the spring.

5. An impact wrench as in claim 4, wherein the cam element is arranged relative to the flange so that the land lies at all times in a plane axially clear of the cam tooth.

6. An impact wrench as in claim 5, wherein the cam element has unitary axial movement with the dog-hammer sufiicient to carry the land of the cam element an axial distance from the cam tooth which is greater than the diameter of the ball.

7. An impact wrench as in claim 6, wherein the ball track is defined by an annular groove in the cam element interrupted by the land and by an opposed parallel annular groove in the flange interrupted by the cam tooth in which ball track the shoulders at the ends of the land define the limits of rollable movement of the ball about the track.

8. An impact wrench as in claim 7, wherein the cam tooth has a crest defined by a small outside radius, a high end of the driving shoulder of the cam element is adapted to have engagement with the ball when the ball attains a position upon the initial portion of the outside radius of the cam tooth in which position the relative surfaces of the driving shoulder and the outside radius engaging the ball are non-parallel, so that upon continued rotation of the cam element relative to the ball and cam tooth the ball is caused to be thrown forwardly and axially over and beyond the crest of the cam tooth, and the dog-hammer is caused to be simultaneously camrned axially and centrifugally accelerated into engagement with the anvil means.

9. An impact wrench comprising anvil means having impact receiving radial jaws and an axially extending spindle provided with a cam flange, a spring upon the spindle forwardly of the cam flange, a rotary dog-hammer reciprocable axially along the spindle between the cam flange and spring against the resistance of the spring to carry radial jaws on a face thereof into rotary impact with the jaws of the anvil, and camming means operable as a consequence of rotation of the dog-hammer relative to the anvil means to force the dog-hammer axially into such impacting relation; wherein the camming means includes a ball track defined in part by an annular groove in the cam flange interrupted by a symmetrical cam tooth having an outside radiused crest projecting axially into the ball track, and in part by an annular opposed groove in the dog-hammer interrupted by a land having symmetrical inside radiused end shoulders, 21 ball rollable about the track by means of a selected one of the shoulders as the dog-hammer rotates in a certain direction relative to the anvil means, the ball being adapted to attain a position on a rearward portion of the crest of the cam tooth under the drive of the selected shoulder and also on the selected shoulder adjacent the land, in which position the opposing contacting surfaces of the crest of the cam tooth and the selected shoulder upon the ball are nonparallel so that the components of force acting upon the ball by the drive of the selected shoulder are directed forwardly in the direction of rotation of the selected shoulder and axially outward relative to the cam tooth, and the dog-hammer having a range of axial movement relative to the cam tooth which exceeds the diameter of the ball.

10. An impact wrench as in claim 9, wherein the land lies in a plane spaced at all times axially clear of the cam tooth, and the end shoulders of the land define the limits of the ball track.

11. In an impact wrench including a driven torque output anvil means, a rotating driving hammer having axial movement into and out of rotary impacting relation with the anvil means, and a spring urging the hammer to a normally retracted condition out of such impacting relation, camming means operable as a consequence of rotation of the hammer to cause periodic axial movement of the hammer into such impacting relation against the resistance of the spring, the camming means comprising a hammer cam element coupled with the hammer, an anvil cam element coupled with the anvil means arranged in opposed relation to the hammer cam element, a ball track defined between the hammer and anvil cam elements, an arcuate land projecting axially from the hammer cam into the track, a cam tooth projecting axially from the anvil cam into the track, a ball rollable about the track, shoulder means at opposite ends of the land limiting at all times the extent of angular movement of the ball relative to the hammer cam element, one of the shoulder means having driving cooperation with the ball as the hammer rotates in a selected direction so as to force the ball about the track and over the cam tooth and as a consequence force the unitary hammer cam element and hammer axially against the resistance of the spring, the hammer cam element having axial movement with the hammer relative to the anvil cam element which exceeds the diameter of the ball permitting free rolling movement of the ball in the ball track following its movement over the cam tooth, and wall means carried by the hammer cam element at all times circumferentially bounding the track so as to confine the ball in the track.

12. In an impact wrench as in claim 11, wherein means is provided spacing the cam elements axially from one another a predetermined distance permitting a slight axial looseness of the ball in the track relative to the cam elements and avoiding axial forces of compression of the cam elements upon the ball.

13. In an impact wrench cam clutch mechanism be tween rotatable drive and driven means comprising a driving cam element rotatable with the drive means, a driven ca-m element rotatable with the driven means arranged in opposed relation to the driving cam element, a ball track defined between the two cam elements, an arcuate land projecting axially from the driving cam element into the track, a cam tooth projecting axially from the driven cam element into the track, a ball rollable about the track, axially extending shoulder means at opposite ends of the land limiting at all times the extent of angular movement of the ball relative to the driving cam element, the driving cam element having axial movement relative to the driven cam element, spring means yieldably resisting such movement, one of the shoulder means having driving cooperation With the ball as the driving cam element rotates in a selected direction so as to force the ball about the track and over the cam tooth and as a consequence force the driving cam element axially relative to the driven cam element against the resistance of the spring means, the driving cam element adapted when so forced to carry the land axially relative to the cam tooth for a distance substantially greater than the diameter of the ball.

14. In an impact wrench as in claim 13, wherein the land lies in a plane spaced at all times axially clear of the cam tooth.

References Cited UNITED STATES PATENTS DAVID H. BROWN, Primary Examiner.

US. Cl. X.R. 64-29 

